Process for the continuous production of alkali salts of the dialkyldithiocarbamic acid

Abstract

An exemplary process for the production of alkali metal salts of dialkyldithiocarbamic acids produced according to the following steps: i) reaction of one or more dialkylamines, carbon disulphide and alkali metal hydroxides to form alkali metal salts of dialkyldithiocarbamic acids; ii) crystallisation to form a crystal suspension of alkali metal salts of dialkyldithiocarbamic acids; iii) separation of crystals of alkali metal salts of dialkyldithiocarbamic acids from the mother liquor in step ii; (iv) recirculation of the separated mother liquor into the crystallisation process; and v) drying of the alkali metal salts of dialkyldithiocarbamic acids.

The invention claimed is: 
     
       1. A process for producing alkali metal salts of dialkyldithiocarbamic acids, comprising the steps:
 i) a reaction step comprising a reaction of one or more dialkylamines, carbon disulphide and one or more alkali metal hydroxides in aqueous solution so as to form an aqueous reaction solution of alkali metal salts of dialkyldithiocarbamic acids; 
 ii) a crystallisation step comprising an introduction of the reaction solution from step i) in an evaporative crystalliser, which is heated by a heater such that a temperature of 30-95° C. is present at the contact surface of the heating element to the reaction solution, and in which a pressure of 10-800 mbar is present, so as to form a crystal suspension of alkali metal salts of dialkyldithiocarbamic acids; 
 iii) a separation step comprising an introduction of the crystal suspension formed in step ii) into a centrifuge and centrifugation of the crystal suspension for solid/liquid separation so as to form crystals of alkali metal salts of dialkyldithiocarbamic acids on the one hand and separated mother liquor on the other hand; 
 iv) a recirculation step comprising a recirculation of the separated mother liquor obtained in step iii) into the crystallisation process; and 
 v) a drying step comprising a drying of the alkali metal salts of dialkyldithiocarbamic acids separated off in step iii), wherein the drying step is designed especially such that the separated alkali metal salts of the dialkyldithiocarbamic acids are dried by means of a contact dryer. 
 
     
     
       2. A process according to  claim 1 , characterised in that one or more of one or more of sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate and potassium dimethyldithiocarbamate is/are formed as alkali metal salt of dialkyldithiocarbamic acids. 
     
     
       3. A process according to  claim 1 , characterised in that the process is performed as a continuous process. 
     
     
       4. A process according to  claim 1 , characterised in that exhaust vapours formed in the crystallisation step ii) are condensed to form a vapour condensate. 
     
     
       5. A process according to  claim 4 , characterised in that, after the condensation of the exhaust vapours to form a vapour condensate, any remaining inert waste gases are washed with water in a waste gas scrubbing, and the washing water is recirculated into the reaction step i). 
     
     
       6. A process according to  claim 5 , characterised in that the vapour condensate is fed back into the reaction step i). 
     
     
       7. A process according to  claim 1 , characterised in that the process is performed such that the drying step is carried out in the contact dryer at a temperature of 30-110° C., and at a pressure of 5-1000 mbar. 
     
     
       8. A process according to  claim 7 , characterised in that the drying step is carried out such that inert, pre-heated carrier gas is conducted through the contact dryer. 
     
     
       9. A process according to  claim 8 , characterised in that the carrier gas is selected from air and/or nitrogen. 
     
     
       10. A process according to  claim 8 , characterised in that the carrier gas, after having been conducted through the contact dryer, is washed with water in a waste gas scrubbing, and the washing water is fed back into the reaction step i). 
     
     
       11. A process according to  claim 1 , characterised in that the individual reaction partners in the reaction step i) are fed into a static mixer, the pressure in the static mixer being greater than the vapour pressure of the particular reaction partner. 
     
     
       12. A process according to  claim 1 , wherein a temperature of 45-80° C. is present at the contact surface of the heating element to the reaction solution, and in which a pressure of 50-400 mbar is present. 
     
     
       13. A process according to  claim 1 , characterised in that the process is performed such that the dry step is carried out in the contact dryer at a temperature of 60-100° C. and at a pressure of 50-200 mbar. 
     
     
       14. A process according to  claim 1 , characterised in that the process is performed such that the dry step is carried out in the contact dryer at a temperature of 60-100° C. and at a pressure of 60-80 mbar.